John Deere Z535M engine surging

[wavinwayne]

I have a new to me John Deere Z535M zero turn mower with 215 hours on it and an unknown service history. This mower has a 25HP Briggs & Stratton 724cc V-twin engine. When I got the mower, the gas tank was empty, and the only gas I have used is 87 octane zero ethanol. Mower seems to be in good shape mechanically but the engine surges when the blades are not engaged. It does not surge with blades engaged. In an attempt to remedy the surging, I've replaced the air filter, spark plugs, fuel filter, and changed the oil+filter using John Deere parts. The surging is still there, no better or worse. Looking for suggestions on what I might try next. The carb on this mower is very difficult to get to and remove (for me), so if the fix involves removing the carb, I guess I will just live with the surging since it doesn't affect the performance while mowing.

 

[bmod305]

Try a couple tanks of gas with Seafoam. Might want to check valve clearance also. Easy to do on Briggs V twin. Ton of YouTube tutorials.

 

[97prizm]

Many come up when you search for this. The main remedy is a fuel blockage or dirty carburetor. Sometimes the fuel pick up tube that sucks fuel out of the float bowl can be partially clogged. Other consistent replies seem to say electrical/grounding issues or problems with the governor. Good luck. Post back if you fix it.

 

[ripcord]

Surging is usually a lean condition. Check the plastic intake manifold for cracks. An easy way is to spray it with carb cleaner while the engine is running.

 

[supton]

Strangely enough, my Cub Cadet was doing this--well, last 3 or 4 cuts that is. Runs fine at full tilt with blades going, but blades off, high or low speed, it would surge.

On a hunch, engine running (and surging), I loosened the air filter. Smoothed right out. I don't think I have 25 hours on that filter, and it looks fine to me. But the engine doesn't think so.

 

[wavinwayne]

Strangely enough, my Cub Cadet was doing this--well, last 3 or 4 cuts that is. Runs fine at full tilt with blades going, but blades off, high or low speed, it would surge.

On a hunch, engine running (and surging), I loosened the air filter. Smoothed right out. I don't think I have 25 hours on that filter, and it looks fine to me. But the engine doesn't think so.

Interesting. No way to do that on this engine, though.

 

[supton]

Interesting. No way to do that on this engine, though.

Maybe just remove and see how it runs? Sorry, not familiar with your engine at all.

 

[Brian123]

Try a product called Mechanic In A Bottle, lots of good reviews on Amazon and Home Depot.

 

[Slick3914]

Some Techron can solve this issue.

 

[wavinwayne]

Maybe just remove and see how it runs? Sorry, not familiar with your engine at all.

I'll try that next time I fire it up.

 

[Soft Cars]

Carburetor. It's the biggest variable of the engine. They have passages and screens that get blocked very easily from contaminated fuel. I try to get people to study up on carburetors. They're fascinating in how they work and it's a very satisfying experience when you get one working the way it's supposed to.

 

[97prizm]

Carburetor. It's the biggest variable of the engine. They have passages and screens that get blocked very easily from contaminated fuel. I try to get people to study up on carburetors. They're fascinating in how they work and it's a very satisfying experience when you get one working the way it's supposed to.

Yeah I had my yard machines push mower looked at. I cleaned the carb, jets, new fuel lines etc. The fuel pick-up tube was partially clogged with residue.

 

[ripcord]

Does it surge at idle? Or only with the engine revved up?

 

[Cujet]

How is the idle? Smooth and steady?

If the carb is not clogged, and the idle is fine, maybe look to see if it has buried idle mixture adjustment screws somewhere.

Not sure if this is the engine. But at 7:35 seconds+ he shows a clogged idle jet.

 

[wavinwayne]

Does it surge at idle? Or only with the engine revved up?

It surges throughout the entire RPM range, but never when blades are engaged.

 

[ripcord]

Usually, if it surges without a load, the low speed/idle circuit in the carb is restricted.

 

[wavinwayne]

Usually, if it surges without a load, the low speed/idle circuit in the carb is restricted.

Assuming I take care of all the other regular maintenance items, is there anything potentially harmful to just accepting/ignoring the surging?

 

[Soft Cars]

It surges throughout the entire RPM range, but never when blades are engaged.

The governor keeps the engine constant while the blades are engaged. When at idle with the blades disengaged, you're having a lean condition from a fuel blockage in the carburetor somewhere. This is a very common occurrence. You notice how I use the the word "occurrence" instead of "problem?" That's because it's not a problem if you like carburetors.

 

[cptbarkey]

This might be highly controversial, but Whip City Wrencher did a recent video and BG44k cleaned a spark plug pretty good vs others. Project Farm also did a video as well. Maybe you can run some in the engine as a try and see thing. I might invest in it as well.

https://www.amazon.com/BG44K-BG-44k-PLATINUM-New/dp/B07PXCTPV7/ref=sr_1_7?crid=6YVZKRGR80GG&keywords=BG+44k+PLATINUM&qid=1640170145&sprefix=bg+44k+platinum%2Caps%2C69&sr=8-7

 

[ripcord]

Assuming I take care of all the other regular maintenance items, is there anything potentially harmful to just accepting/ignoring the surging?

Possibly. Gasoline engines run hotter when lean which is not good for them. You have an increased risk of burning valves and blowing head gaskets.

I would try running some fuel cleaner through it and see if that does the trick. I like Berryman's B12.